The invention relates generally to editing digital video streams, or files.
FIG. 1 illustrates how many current digital video cameras generate a digital video formatted (DV) data stream. As light passes though a digital camera""s lens it is split into red, green, and blue (RGB) components and sampled by a charge coupled device, CCD (block 100). CCD output signals are digitized by sampling the captured image both horizontally and vertically (block 102). A standard vertical sample rate is 525 lines and a standard horizontal sample rate is 500 pixels per line. At this point, each pixel contains a measurement for the red, green, and blue components of the light that is incident on its corresponding CCD element. Data rates following CCD sampling may be approximately 31 MBps (megabytes per second).
A pixel""s RGB values may then be converted to the YUV color space CS (block 104), where Y represents a pixel""s brightness, and U and V its color values. Typically, each pixel""s Y values are sampled four times, while a pixel""s U and V values are sampled twice. The resulting signal is often referred to as a YUV 4:2:2 video signal. Conversion from the RGB to YUV color space in this manner may reduce the video stream""s data rate to approximately 20.5 MBps.
The YUV 4:2:2 signal is generally reduced to YUV 4:1:1 to coincide with the National Television Standards Committee (NTSC) video standard (block 106). In this reduced format, a pixel keeps its own unique Y brightness information, but groups of four neighboring pixels share the same U and V color information. Reducing the video signal from YUV 4:2:2 to YUV 4:1:1 is designed to reduce the video signal data rate to approximately 15.5 MBps. Intraframe compression is then applied to generate a digital video signal whose data rate is approximately 3.1 MBps (block 108).
While some DV tools allow a user to edit DV data streams digitally, they are generally slow because they operate on raw DV data streams. At a generation rate of 3.1 MBps, even a relatively short video of an hour requires approximately 11 GB (gigabytes) of storage. Not only do most users not have this much permanent storage, manipulating (i.e., editing) data streams this large on a standard personal computer may be a very slow process. Thus, it would be beneficial to provide a mechanism to edit DV data streams that use less disk space while also increasing editing performance.
In one embodiment, the invention provides a technique to edit image data. The technique includes receiving image data in a first format, converting the received image data into a second format, editing the received image data in the second format to generate a sequence of edit commands, and generating image data in a third format based on the sequence of edit commands.